In the case of an autostereoscopic image display apparatus, a viewer (user) can view a stereoscopic image with naked eyes without using special glasses. In such a stereoscopic image display apparatus, a plurality of images which differ in viewpoint are displayed on a plane display device (for example, a liquid crystal display device) and light rays from these images are controlled by an optical plate such as a parallax barrier or a lenticular lens. As a result, the viewer views a stereoscopic image. In general, the optical plate is provided in front of the plane display device. The controlled light rays are led to both eyes of the viewer. If the viewing position of the viewer is adequate, the viewer can view a stereoscopic image. A zone of viewing positions where such a stereoscopic image can be visually recognized is referred to as viewing zone.
However, there is a problem that such a viewing zone is limitative. In other words, there is a pseudoscopy zone formed of viewing positions where, for example, a viewpoint of an image perceived by a left eye is located relatively on the right side as compared with a viewpoint of an image perceived by a right eye and consequently it becomes impossible to perceive a stereoscopic image correctly. In an autostereoscopic image display apparatus, therefore, a normal stereoscopic image cannot be viewed in some cases depending upon the viewing position of the viewer.
Therefore, it is conducted to enable viewing a correct stereoscopic image by providing a sensor on a stereoscopic image display apparatus to detect the position of the viewer, displaying an image as it is when the viewer is judged to be located in a viewing zone on the basis of an output of the sensor, and controlling a display image to cause an image for the right eye and an image for the left eye to be incident respectively upon the right eye and the left eye of the viewer when the viewer is judged to be located in the pseudoscopy zone.
In general, a camera is used as the sensor. In a conventional stereoscopic image display apparatus having such a camera, a stereoscopic image displayed on the stereoscopic image display apparatus varies depending upon the position of the viewer. Further, in some cases, although any one of a plurality of viewers does not move from the position, it is recognized on the basis of an image picked up by the camera that at least one viewer is moving, and consequently a stereoscopic image is changed over. In this case, it is a problem that the stereoscopic image is changed over to viewers other than the viewer recognized as moving.